Method for producing a plate

ABSTRACT

In a process for the production of a plate, in particular a motor vehicle licence plate, in which at least a layer sequence forming an electroluminescence flat capacitor ( 4, 5, 6, 7 ) and a reflection film ( 10; 10 ′) are applied to a carrier ( 1 ), a reflection film ( 10; 10 ′) is selected whose reflection value is higher than the maximum value permitted by statute, and said reflection value is reduced by further production steps to such an extent that it is below the maximum value permitted by statute.

BACKGROUND OF THE INVENTION

The invention concerns a process for the production of a plate, inparticular a motor vehicle licence plate, and plates produced inaccordance with that process.

Reflective plates, in particular motor vehicle licence plates, are knownfrom the state of the art, the reflectance of which is based on areflection film being glued or laminated on to a carrier which forexample comprises sheet aluminum. In that situation it is necessary touse reflection films whose reflectance is within a range which is fixedby statute and which establishes that the reflectance may not fall belowa minimum value of that range or exceed a maximum value thereof.Commercially available films which satisfy those conditions include acarrier layer which frequently comprises aluminum and which isimpenetrable for light.

If now the attempt is made to produce a plate, in particular a motorvehicle licence plate, which is self-illuminating by virtue of the factthat, on one of its flat sides, it has a layer sequence which forms anelectroluminescence flat capacitor and which is constructed directly onthe plate itself, then in accordance with the state of the art such aplate cannot be at the same time designed to be reflective. Morespecifically, if the layer sequence of the flat capacitor is firstlyapplied to the carrier, it cannot then be covered over with theabove-mentioned reflection films as the carrier thereof does nottransmit the light which it emits.

If conversely the attempt is made to apply a surface-coveringelectroluminescence flat capacitor arrangement to the top side of areflection film applied to the plate carrier, the reflection propertiesthereof become ineffective as at least some of the flat capacitor layersare impenetrable in both directions in relation to external light.

Admittedly transparent reflection films are also available on themarket, but they have a reflectance which is substantially higher thanthe above-mentioned maximum value which is permitted by statute.

SUMMARY OF THE INVENTION

In comparison therewith the object of the present invention is toprovide a process of the kind set forth in the opening part of thisspecification, which makes it possible easily and inexpensively toproduce plates, in particular motor vehicle licence plates, which have areflectance complying with the statutory requirements and which at thesame time carry an electroluminescence flat capacitor which covers atleast the major part of the flat side thereof and which impartsself-illuminating properties thereto.

To attain that object, the invention provides the features recited inthe appended claims.

Those features are based on the consideration that it is possible toapply both a layer sequence forming an electroluminescence flat orsurface capacitor and also a reflective film to one and the same side ofthe carrier, if a reflection film is used, whose reflectance isinitially higher than the maximum value permitted by statute, but thatreflection foil is subjected to at least one manufacturing step which atleast in location-wise manner reduces its reflectance to such an extentas to afford an average value which complies with the statutoryrequirements.

Basically, two different operating procedures are possible when carryingout the method according to the invention.

In one procedure firstly the reflective foil is applied to the carrierof the plate and, on the front side of said film which faces towards theperson viewing it, there is constructed a rastered flat capacitorarrangement, the size and the surface density of the electricallyconductingly interconnected raster points which are impermeable toexternal light being so selected that they cover a sufficient area ofthe reflection film to reduce the mean reflection value thereof to belowthe maximum value permitted by statute and at the same time form asufficiently large area which lights up in operation to satisfy thestatutory requirements in terms of brightness of a self-illuminatingplate. It has surprisingly been found that such a choice in terms ofsize and surface density is possible. With this variant it is immaterialwhether the reflection film has an opaque carrier layer or not.

In a more greatly preferred variant however firstly the layer sequenceforming the flat capacitor is built up on the carrier of the plate andthen covered over with a reflection film which from the outset istransparent or is made transparent in a location-wise manner, for thelight emitted in operation by the flat capacitor.

In order to reduce the initially very high reflection value of such afilm to bring it into the permissible range, a plurality of differentprocess steps which are independent of each other or which can be usedin conjunction with each other are available in accordance with theinvention.

In accordance with a particularly preferred mode of operation atransparent reflection film, at the rear side of which prismaticstructures freely project, at the interfaces of which the light incidentfrom the front side is reflected by total reflection, is so connected toa layer which is applied to the top side of the flat capacitor and whichpreferably at the same time serves as an adhesive for the reflectionfilm and which involves approximately the same refractive index as theprismatic structures of the reflection film, that the free spacespresent between the projecting prismatic structures are at leastpartially filled by said layer. No further total reflection can thenoccur at all the interfaces of the prismatic structures which arecovered by that layer. By virtue of the fact that not all interfaces ofthe prismatic structure are brought into contact with that layer, thereis still a reflectance—although reduced—which can be controlled withinwide limits and in particular in such a way that the statutory standardsare satisfied, by virtue of the extent to which the prismatic structuresare covered by the above-mentioned layer.

That extent can be specifically and targetedly influenced by virtue ofthe production process being of a suitable nature.

In accordance with another preferred process, a transparent reflectionfilm is tempered, that is to say heated, either prior to or during theapplication to the uppermost layer of the flat capacitor or atransparent layer disposed thereover, and/or is pressed against a hardflat surface in such a way that the prismatic structures projecting atthe rear side thereof are flattened off and thus there is a reduction inthe surface regions of said structures, which implement totalreflection. By virtue of suitable selection of the temperature and/orthe pressing pressure as well as the treatment time, it is in turnpossible to reduce the reflectance of the reflection film to such anextent that it is in the range permitted by statute.

A further preferred possibility involves applying a reflection filmwhich is not transmissive in respect of the light of theelectroluminescence flat capacitor on or over the electroluminescenceflat capacitor which is provided with a raster pattern of holes in whichthe size and surface density of the through holes are so selected thatthe reduction implemented thereby in respect of the reflection valuewhich is averaged in relation to surface area reduces same to below thepermitted maximum value and at the same time affords adequate optionsfor transmission of the light emitted by the flat capacitor inoperation, in order to be able to satisfy the statutory brightnessrequirements.

The features of plates which are produced in accordance with one of theprocesses of the invention are set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described hereinafter by means of embodiments by way ofexample with reference to the drawing in which:

FIG. 1 shows a diagrammatic cross-section through a first embodiment ofa plate according to the invention in which the degree of reflection ofa transparent reflection film is reduced by partially immersing theprismatic structures projecting on the rear side in an adhesive layerhaving the same refractive index,

FIG. 2 shows a diagrammatic cross-section through a second embodiment ofa plate according to the invention in which the degree of reflection ofa transparent reflection film is reduced by completely immersing theprismatic structures projecting on the rear side in an adhesive layerwhich is only partially applied to the surface of the plate and havingthe same refractive index,

FIG. 3 shows a diagrammatic cross-section through a third embodiment ofa plate according to the invention in which the degree of reflection ofa reflection film having a non-transparent carrier is reduced byapplying a grid raster of holes which pass through to theelectroluminescence flat capacitor, and

FIG. 4 shows a diagrammatic cross-section through a fourth embodiment ofa plate according to the invention in which the degree of reflection ofa transparent reflection film is reduced by flattening or rounding ofthe prismatic structures projecting on the rear side.

DETAILED DESCRIPTION OF THE INVENTION

In all illustrated embodiments the thicknesses of the individual layersare not shown true to scale and in part, for the sake of simplicity, areillustrated on a greatly enlarged scale. The prismatic structures whichproject from the rear side of the reflection film or which are embeddedinto the reflection film and at the interfaces of which reflection ofthe light incident from the front, that is to say from above in theFigures, are shown in greatly simplified form as rearwardly projectingprisms of triangular or trapezoidal cross-section.

In the lower region all illustrated embodiments involve the same layerstructure. Those layers which are the same in all of FIGS. 1 through 4are denoted by the same references.

The basis of each plate is formed by a deformable carrier 1 which cancomprise a plastically deformable plastic material or metal, for examplealuminum. In the latter case the carrier 1 is preferably completelycovered over by an insulating layer 2 which on its top side carries ametal coating which is a good electrical conductor, for example ofcopper, and out of which are etched various conducting regions of whichthe Figures show in cross-section only the region forming the baseelectrode 4 of the electroluminescence flat capacitor describedhereinafter. If a plurality of mutually juxtaposed, separately actuableflat capacitors are to be provided on the plate, then a plurality ofmutually electrically insulated base electrodes with their respectiveactuating lines can also be etched out of the metal coating. Inaddition, a feed-in line (not shown) for the transparent cover electrodeof the flat capacitor or capacitors, said electrode being described ingreater detail hereinafter, is also advantageously etched out of themetal coating in such a way that it is electrically insulated from thebase electrode or electrodes and the actuating lines thereof.

Disposed over the metal coating is an insulating layer 5 which coversthe entire surface of the base electrode 4 and which is preferablycolored with a light pigment so that the light which is emittedrearwardly, that is to say downwardly in the Figures, by the pigmentlayer 6 disposed thereabove in operation of the flat capacitor isradiated as completely as possible forwardly. Disposed over the pigmentlayer is a transparent, extremely thin cover electrode 7 which howeveris a good electrical conductor and which, in at least one edge region(not shown in the Figures) in which the insulating layer 5 and thepigment layer 6 are omitted, is in good electrically conducting contactwith the feed-in line which is produced from the metal coating so thatan ac voltage can be applied by way of that feed-in line to the coverelectrode 7 in relation to the base electrode 4, by virtue of whichvoltage the doped pigments contained in the pigment layer 6 are excitedin known manner to produce a light referred to as electroluminescence.

The structures described hereinbefore can be produced by a procedurewhereby a commercially available film which forms the insulating layer 2and which is provided on its underside with an adhesive layer (notshown) and which on its top side carries the metal coating is glued orlaminated on to the carrier 1. The operation of etching out the various,electrically mutually separated line and electrode regions can beeffected as required prior to or after that operation of applying theplastic film to the carrier 1. The further layers 4 through 7 of theflat capacitor can be applied by known coating processes (spraying,screen printing, thick layer or other coating processes).

In the embodiment shown in FIG. 1, disposed over the transparent coverlayer 7 is a comparatively thick adhesive layer 9 which is applied overthe entire flat side of the plate and which serves for fixing thereflection film 10 disposed thereover. The adhesive used for theadhesive layer 9 at least in the hardened final condition has arefractive index which is substantially equal to the refractive index ofthe prismatic structures 12 projecting from the rear side of thereflection film 10. When applying the reflection film 10 it is pressedunder a predetermined pressure in such a way that those prismaticstructures 12 penetrate to a desired depth into the adhesive layer 9.For all light beams which impinge on the transparent reflection film 10from the front, that is to say from above in the Figures, and which arepropagated therethrough into the prismatic structures 12, no or only agreatly reduced level of total reflection occurs at the surface portionsof the prismatic structures 12 which are covered by the adhesive of theadhesive layer 9, because of the equal or almost equal refractiveindices; total reflection however is retained unreduced at the surfaceportions of the prismatic structures 12, which are not covered byadhesive. On average therefore that affords a reflectance on the part ofthe reflection film 10, which is reduced in comparison with thenon-adhesive-coated condition thereof. The extent of the reduction inthe reflectance depends on the depth of immersion of the prismaticstructures 12 into the adhesive layer 9, which in turn can be controlledby the pressure exerted in the operation of applying the reflection film10 and/or the viscosity of the adhesive which prevails at the time ofapplying the reflection film. It is thus possible to use a reflectionfilm 10 which is very substantially transparent for the light of theflat capacitor or capacitors and which, prior to processing thereof, hasa very high reflectance which is above the maximum value permitted bystatute, that reflectance being reduced in a specific targeted fashionin production of the plate in such a way that it falls in the rangewhich is permitted by statute.

The embodiment shown in FIG. 2 only differs from that shown in FIG. 1 inthat the adhesive layer 9 is not applied over the entire surface areabut only partially to the top side of the transparent cover electrode 7and that the prismatic structures 12 projecting at the rear side of thereflection film 10, in the surface regions in which there is an adhesivelayer 9, are immersed completely into same so that the free spacesbetween them are entirely filled with adhesive. Therefore, no totalreflection whatsoever takes place in those regions at theadhesive-covered surfaces of the prismatic structures 12. In contrast,in the surface regions in which there is no adhesive layer 9, theprismatic structures 12 retain their capability of total reflection tothe full extent. Accordingly, by virtue of a suitable choice both of thesize and also the distribution of the surface regions which are coveredwith an adhesive layer 9 and the adhesive-free surface regions disposedtherebetween, it is possible to achieve a mean reflectance in respect ofthe reflection film 10, which is within the range permitted by statute,although the reflectance of the reflection film 10 before processingexceeds the maximum permissible limit value.

The adhesive layer 9 can be applied in different ways both in theembodiment of FIG. 1 and also in the embodiment shown in FIG. 2.

One possible way involves using a screen printing process which makes itpossible quickly and reliably to implement both application over theentire surface area as shown in FIG. 1 and also the application limitedto individual surface regions, with interposed adhesive-free surfaceregions, in an economical fashion.

Another process involves using a transfer film which is covered on oneside with an adhesive layer or an adhesive pattern and which is pressedwith that layer leading against the uppermost layer of the flatcapacitor or a layer covering the flat capacitor in order to transferthe adhesive on to that layer. Thereafter, the transfer film is detachedand the reflection film is applied.

Another possibility involves using an adhesive film which is coated withadhesive on both sides, wherein the adhesives on the two flat sides ofthe adhesive film can be the same or, adapted to the specific conditionsinvolved, can be different from each other. Thus, particularly in thecase shown in FIG. 2, the lower adhesive layer is distributed over theentire surface area while only individual surface elements are coveredwith adhesive on the top side of the adhesive film. The layerthicknesses of the adhesives on the two sides of the adhesive film canbe the same or different from each other. Using the lower adhesivelayer, the adhesive film is stuck on to the uppermost layer of the flatcapacitor or a layer covering same, while the reflection film is gluedon to the top side of the adhesive film. As the adhesive film remains inthe layer structure of the plate, it must be transparent in relation tothe light emitted by the flat capacitor in operation.

The embodiment shown in FIG. 3 uses a reflection film 10′ whichcomprises three layers, namely a foremost transparent cover layer 14which in turn includes prismatic structures 12 which are completelyembedded into an intermediate layer 15 which is also transparent and therefractive index of which differs from that of the prismatic structures12 so greatly that total reflection occurs at the interfaces. Thereflection film 10′ further includes a carrier layer 16 comprising amaterial which is not transparent for the light of the subjacent flatcapacitor 4 through 7, for example aluminum, which is stuck by means ofan adhesive layer (not shown) on to the top side of the transparentcover layer 7 or laminated thereon in some other fashion.

In order here to reduce in the required fashion the initially very highreflectance of the reflection film 10′, which is above the statutorylimit value, the reflection film 10′ is provided with a grid raster ofthrough holes 19, that is to say holes which extend through all layers14 through 16, only some of the holes being shown in FIG. 3. Thediameter and the surface density of the holes 19 are on the one hand soselected that the reflectance of the reflection film 10′ is reduced inthe required fashion and at the same time sufficient light can issuefrom the flat capacitor 4 through 7 forwardly (that is to say upwardlyin the Figures) in order to satisfy the statutory requirements in regardto the brightness of an illuminated plate, in particular a motor vehiclelicence plate.

The embodiment illustrated in FIG. 4 again uses a reflection film 10which is transparent in relation to the light of the flat capacitor 4through 7 and from the rear side of which the prismatic structures 12freely project. It is stuck on to the top side of the transparent coverelectrode 7 with a thin adhesive layer 20 which here does not penetrateinto the intermediate spaces between the prismatic structures 12. Inorder nonetheless to achieve the required reduction in the reflectanceof the reflection film 10, those prismatic structures 12 are flattenedoff or rounded in such a way that, in the cross-section in FIG. 4, theyare of a substantially trapezoidal configuration, whereby their surfaceregions permitting total reflection are reduced in size.

Flattening or rounding of the prismatic structures 12 can be effected bythe film 10 being heated and pressed against a hard surface under apredetermined pressure. The extent of the flattening or rounding effectcan be controlled by the level of the temperature used and/or themagnitude of the pressing pressure. It will be appreciated that, themore the prismatic structures 12 are flattened off, the greater will bethe reduction in the reflectance of the film 10.

Depending on the respective nature of the reflection film used howeverit may also be sufficient for it just to be heated to an elevatedtemperature for a given period of time in order to achieve the desiredflattening or rounding of the prismatic structures, without pressurehaving to be applied at the same time to the film or the prismaticstructures.

When using other films, it may be sufficient only to exert a givenpressure on the prismatic structures without in that respectspecifically increasing the temperature. In this case also the period oftime and the magnitude of the pressure can be employed as controlparameters.

In all those cases, the operation of heating and/or pressing the film 10can be effected either in a separate step in the process prior to theapplication thereof to the cover electrode 7 or a layer covering same,or during that application procedure.

All the illustrated embodiments may include additional layers, inparticular protective layers for covering the outward sides, which arenot shown in the Figures. As an alternative to the embodiment shown inFIG. 1 it is also possible to apply pressure to the transparentreflection film 10 in such a way that the tips of the prismaticstructures which project at the rear side thereof penetratingly advanceas far as the cover electrode 7 or a transparent hard layer (not shown)disposed thereover, but substantially cannot deform same, because of itshardness. In that case the thickness of the adhesive layer 9 which iscompletely pierced by the prismatic structures 12 is so selected that itonly partially fills in respect of height the free spaces presentbetween those prismatic structures, and thus reduces the reflectance ofthe reflection film 10 not completely but to the desired extent.

The measures described hereinbefore by means of the embodiments by wayof example in FIGS. 1 and 2 can also be adopted in combination. It isalso possible to provide adhesive layers of differing thicknesses indifferent surface regions, those adhesive layers filling to differentheights the free spaces between the prismatic structures 12.

Another possibility involves applying the layers of the flat capacitornot under the reflection film 10 or 10′ but on the top side thereofwhich is towards the person viewing the arrangement, in rastered form.As those layers do not transmit any light to the reflection film 10 or10′ or light reflected thereby cannot issue through the top side, asuitable choice in respect of the size and surface density of theelectrically conductively interconnected raster points of the flatcapacitor arrangement reduces the mean reflectance of the reflectionfilm 10 or 10′ in the desired manner and at the same time achieves therequired brightness of the flat capacitor arrangement. In that case itis possible to use both completely transparent reflection films 10 andalso reflection films 10′ which include an opaque layer.

1. A process for the production of a plate, in particular a motor vehicle licence plate, in which initially at least one layer sequence forming an electroluminescence flat capacitor (4, 5, 6, 7) and thereafter a reflection film (10; 10′) which is translucent for the light of the electroluminescence flat capacitor (4, 5, 6, 7) are applied to a carrier (1), wherein the reflection value of the reflection film (10; 10′) is higher than the maximum statutory permissible value, and said reflection value is reduced by further production steps to such an extent that it is below the maximum statutory permissible value, characterised in that a reflection film (10) is used whose reflection properties are based on it having on its rear side rearwardly projecting prismatic structures (12), at the interfaces of which the light incident from the front side is reflected by total reflection, and that the further production steps involve applying the reflection film (10) to an adhesive layer (9) which is translucent in respect of the light of the electroluminescence flat capacitor (4, 5, 6, 7) and is of approximately the same optical refractive index as the rearwardly projecting prismatic structures (12) of the reflection film (10), and in that situation the intermediate spaces between the prismatic structures (12) are partially filled by the adhesive to such an extent that the reflection value of the reflection film (10) is reduced in the desired manner.
 2. A process as set forth in claim 1, characterised in that the operation of filling the intermediate spaces between the prismatic structures by the adhesive is partially effected in respect of height by a procedure whereby the pressing pressure of the reflection film (10) and the viscosity of the adhesive at the time of pressing the reflection film (10) are so selected that the prismatic structures (12) which project on the rear side of the reflection film (10) penetrate into the adhesive only to such a depth that the total reflection which is reduced in the regions embedded in the adhesive reduces the reflection value of the reflection film (10) in the desired fashion.
 3. A process as set forth in claim 1, characterised in that filling of the intermediate spaces between the prismatic structures (12) by the adhesive is effected partially in respect of height by the adhesive being applied to a layer which is so hard that it is substantially not deformable by the prismatic structures (12) projecting from the rear side of the reflection film (10) when the reflection film produced is subjected to pressure and by the thickness of the adhesive layer being so selected that the prismatic structures (12) which project on the rear side of the reflection film (10) and which when pressure is applied to the reflection film (10) penetrate with their tips as far as the hard layer engage into the adhesive only to such a depth that the total reflection which is reduced in the regions embedded in the adhesive reduces the reflection value of the reflection film (10) in the desired manner.
 4. A process as set forth in claim 1, characterised in that filling of the intermediate spaces between the prismatic structures (12) by the adhesive is effected partially in respect of surface area in that, in surface regions disposed in mutually juxtaposed raster-like relationship, the intermediate spaces between the prismatic structures (12) are filled to differing heights so that the reflection value of the reflection film (10), which is averaged in respect of surface area, is below the maximum value permitted by statute.
 5. A process as set forth in claim 4, characterised in that in first surface regions the intermediate spaces between the prismatic structures (12) are filled completely in respect of height by the adhesive while in the interposed second surface regions there is no filling of the intermediate spaces by the adhesive.
 6. A process as set forth in claim 2, characterised in that filling of the intermediate spaces between the prismatic structures (12) by the adhesive is effected partially both in respect of height and also in respect of surface area.
 7. A plate, in particular a motor vehicle licence plate, which includes a carrier (1), a reflection film (10; 10′) and at least one layer sequence which as seen from the viewer is disposed behind the reflection film (10′) and which forms an electroluminescence flat capacitor (4, 5, 6, 7), wherein the reflectance, which is originally above the maximum value permitted by statute of the reflection film (10; 10′) which is translucent for the light of the electroluminescence flat capacitor (4, 5, 6, 7), has been reduced in the course of the plate production process, characterised in that prismatic structures (12) which project from the rear side of the reflection film (10) and at the interfaces of which the light incident from the front side is reflected by total reflection are partially embedded into a transparent layer (9) having approximately the same refractive index as the prismatic structures (12), in such a way as to afford a reduced total reflectance.
 8. A plate as set forth in claim 7, characterised in that partial embedding is based on the fact that the prismatic structures (12) are not engaged over their entire height into the transparent layer (9) having approximately the same refractive index.
 9. A plate as set forth in claim 7, characterised in that the prismatic structures (12) in differing surface regions of the flat side of the plate are engaged to differing depths into the transparent layer (9) having substantially the same refractive index.
 10. A plate as set forth in claim 9, characterised in that in first surface regions of the flat side of the plate the prismatic structures (12) are engaged with their entire height into a transparent layer (9) having substantially the same refractive index and in second surface regions they are not engaged into such a layer.
 11. A plate as set forth in claim 7, characterised in that the layer (9) having substantially the same refractive index is an adhesive layer which serves at the same time for fixing the reflection film (10) on the layer therebeneath. 